The invention relates to a hybrid twin-clutch transmission and to a method for controlling this transmission.
A hybrid twin-clutch transmission for a motor vehicle is disclosed in DE 198 50 549 A1, for example. The twin-clutch transmission comprises a twin-clutch arrangement with a first clutch and a second clutch and also with an input side for connecting the twin-clutch arrangement to an engine. The twin-clutch transmission furthermore comprises a first input shaft and a second input shaft which are arranged on an output side of the twin-clutch arrangement.
The twin-clutch transmission of DE 198 50 549 A1 can be connected to an output drive by means of an output shaft. For connecting the first or the second input shaft to the output shaft, a number of gearwheel pairs are provided, by means of which a torque can be transmitted between one of the input shafts and the output shaft when a gear-shifting clutch assigned to the gearwheel pair concerned is closed. The twin-clutch transmission furthermore comprises a first electric machine and a second electric machine which are connected to the first input shaft and to the second input shaft respectively. These electric machines can perform very different functions, such as synchronizing the rotational speed of one of the input shafts with the rotational speed of the output shaft, for example.
DE 198 50 549 A1 proposes using one or both of the electric machines for starting the engine in order consequently to dispense with the otherwise usual starter. If both electric machines are to be used, both clutches must therefore be closed for transmitting a starting torque to the crankshaft of the engine.
However, hydraulically actuated clutches are also used in twin-clutch transmissions. In this connection, the clutches can be designed in such a way that a certain hydraulic pressure must be applied for closing them. However, if the hydraulic pressure is built up with the aid of the internal combustion engine, the clutches cannot be used for starting the (still idle) engine. The arrangement disclosed in DE 198 50 549 A1 of the electric machines cannot therefore be used for starting with all possible clutch types.